Multinuclear magnetic resonance study of some imidovanadium complexes

N-14 NMR studies were carried out for a series of mononuclear and dinuclear vanadium complexes with different types of nitrogen ligands (terminal and mu-imido, amido, nitrido, amine). Some complexes containing ancillary phosphine moieties were also characterized by P-31 NMR spectroscopy. The observed shieldings for terminal and bridging imido ligands are intermediate between those of nitrido and amido moieties, and the latter appear less shielded than coordinated tertiary amines. The ranges for individual ligand types are sufficiently resolved to allow the use of nitrogen chemical shifts as a structure assignment tool. The N-14 NMR signals of terminal and bridging imido nitrogens displayed marked differences in their lineshapes which could be used as an additional criterion for signal assignment. Examination of substituent influences revealed the absence of a general parallelism between delta(14)N and delta(51)V, but gave evidence for parallel relationships between both quantities for complexes with formal 12VE and 16VE electron counts. Determination of (1)J(V-51,(14) N) and (1)J(V-51,P-31) coupling constants in mononuclear complexes was feasible from simulation of N-14 and P-31 lineshapes and suggested that imido ligands exhibit generally greater couplings to vanadium than amido ligands. Analysis of the P-31 {H-1,N-14} NMR spectrum allowed us to determine (2)J(V-51,P-31) for the vanadacycle cyclo((BuN)-Bu-t-P=C(Bu-t) -VCl3-). It was shown that both couplings can be employed for the acquisition of two-dimensional P-31,V-51 shift correlations. Copyright (C) 2001 John Wiley Sons, Ltd.